Hybrid power systems employing multiple power energy sources require careful control of system components in order to coordinate the delivery of power from the sources to system loads. These loads can vary widely in magnitude, and occur unexpectedly in time, particularly in hybrid powered vehicles. Hybrid systems using fuel cells and battery packs as energy sources to power vehicles must be closely controlled to assure adequate reserve power is available under a variety of conditions, including having available sufficient power to start a hybrid vehicle after long period of non-use, or during electric-drive-only modes of operation.
In order to assure that adequate power is present in the a hybrid vehicle's traction battery pack and that proper charging and discharging of the battery is maintained, the state-of-charge (SOC) of the battery is monitored, and charging and discharging are controlled so that the SOC remains within an acceptable range or “window”. When the SOC is low, the fuel cell may be called upon to produce power in order to charge the battery to keep the SOC within the desired window.
Typically, an auxiliary charge storage device such as a battery is used for starting the engine in a hybrid vehicle while another charge storage device such as the HV traction battery is used alone or in combination with an internal combustion engine for powering of the vehicle. The HV traction battery may partially discharge over extended periods of non-use, during electric drive only operations when only the HV traction battery is powering the vehicle, or during repeated stop and start operation where the HV traction battery is repeatedly used. Consequently, the performance of the vehicle may be compromised.
In the prior art, solar as well as plug-in power systems have been proposed for the recharging of an on-board vehicle battery.
For example, in U.S. Pat. No. 4,327,316, a rechargeable auxiliary battery formed by solar batteries is used to charge a vehicle battery using recharging current means. The charging system is used to avoid discharge of the battery during extended periods of non-use or when repeated vehicle stop operations are required.
In U.S. Pat. No. 4,564,799, a dual battery system is used wherein a secondary battery is charged by a secondary power source which is a solar cell. The secondary battery is used to start the motor (e.g., for the ignition device) to improve the starting performance of the vehicle.
In U.S. Pat. No. 4,581,572 a solar battery independent of the vehicle battery is used to increase the output of an AC (alternating current) generator used for recharging the vehicle battery.
In U.S. Pat. No. 5,162,720 a supplemental utility AC source such as a 110V duplex outlet is used together with a converter to allow recharging of an auxiliary battery. Charging current may flow in one direction from the auxiliary battery to the engine battery to reduce the risk of the engine battery becoming too depleted to start the vehicle engine.
U.S. Pat. Nos. 6,222,341 and 6,452,361 discuss a vehicle including a dual battery system where a reserve battery is used together with charge maintenance devices to produce a relatively low charging rate to a starting battery during periods where the vehicle is not in use or when the starting battery requires additional charge. The reserve battery is charged by the vehicle alternator.
Other prior art sources have generally proposed recharging the primary vehicle battery by means of solar power or AC utility.
In order to overcome the problem of depletion of a hybrid vehicle charge storage device such as a high voltage (HV) traction battery, it would be advantageous to provide a system and method to avoid undesired depletion of the HV traction battery, as occurs for example, during extended periods of non-use of the vehicle or during electric-drive-only modes of operation of the hybrid vehicle.
It is therefore an object of the invention to provide a system and method to avoid undesired depletion of a charge storage device such as the HV traction battery, as occurs for example, during extended periods of non-use of the vehicle or during electric-drive-only modes of operation of the hybrid vehicle.